The present embodiments relate to a down converting element based on organic fluoropolymer material. It finds particular application in conjunction with solid state light emitting devices, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Light emitting diodes (LEDs) are well known solid-state, or semi-conductor devices that can generate light having a peak wavelength in a specific region of the visible spectrum. More recently developed LEDs emit blue to ultraviolet (UV) light.
Recently, techniques have been developed for converting the light emitted from LEDs to useful light for illumination purposes. In one technique, the LED is coated or covered with a phosphor layer. A phosphor is a luminescent material that absorbs radiation energy in a portion of the electromagnetic spectrum and emits energy in another portion of the electromagnetic spectrum. Phosphors of one important class are crystalline inorganic compounds of very high chemical purity and of controlled composition to which small quantities of other elements (called “activators”) have been added to convert them into efficient fluorescent materials. With the right combination of activators and inorganic compounds, the color of the emission can be controlled. Most useful and well-known phosphors emit radiation in the visible portion of the electromagnetic spectrum in response to excitation by electromagnetic radiation outside the visible range.
By interposing a phosphor excited by the radiation generated by the LED, light of a different wavelength, e.g., in the visible range of the spectrum, may be generated. Colored LEDs are often used in toys, indicator lights and other devices. Continuous performance improvements have enabled new applications for LEDs of saturated colors in traffic lights, exit signs, store signs, and the like.
In addition to colored LEDs, a combination of LED generated light and phosphor generated light may be used to produce white light. The most popular white LEDs include blue emitting GaInN chips. The blue emitting chips are coated with a phosphor that converts some of the blue radiation to a complementary color, e.g. a yellowish emission. Together, the blue and yellowish radiation produces a white light. There are also white LEDs that utilize a near UV emitting chip and a phosphor blend including red, green and blue-emitting phosphors designed to convert the UV radiation to visible light.
For mechanical integrity, phosphor powders are typically integrated into or coated onto a transparent substrate. Desirably, such substrates should have greater than 90% transparency for the 254-750 spectral region and long term stability (mechanical, thermal and photochemical) under exposure of UV radiation at elevated temperatures. Very few materials satisfy the above requirements to be suitable substrates for the phosphor powder. Therefore, identification of practical, non-fragile, UV and thermal resistant materials for the phosphor carrier in solid state lighting (SSL) applications and phosphor down converting improvement is necessary.
A well-known PMMA plastic (acrylic) has very low upper service temperature ˜90 C and cannot practically be employed for outdoor applications. Some silicones may be considered as suitable materials; however they do not possess sufficient mechanical rigidity. Various types of glasses fit the requirements and are used as phosphor carriers for design and manufacture light sources in lighting industry and can also be incorporated into solid state lighting devices, but glass is often too fragile for most applications. For example, U.S. Patent Application (Pub. No. US 2005/0274967 A1) proposed utilizing inorganic materials like glass as a phosphor down converting material carrier; however glass fragility is an essential disadvantage to this approach.
Therefore, it would be desirable to develop a down converting element that can be effectively used in phosphor down converting applications that is practical, non-fragile and resistant to ultraviolet degradation.